The invention relates to spray apparatus and more particularly to injected liquid chemical spray apparatus or use in agriculture or horticulture.
As an aid to precision farming it is known to provide chemical spray apparatus arranged to vary the rate at which a desired chemical is applied (for example according to local conditions or the ground speed of the spray apparatus) by injecting the chemical directly into the spray liquid e.g. water shortly before it is applied. In this the volume of spray liquid sprayed remains substantially constant in terms of volume per unit area and only the concentration of the sprayed chemical in the spray liquid is varied.
It is known that chemical injection systems may operate with high or low pressure injection pumps. A high pressure injection pump can inject chemical close to the spray nozzle as it has sufficiently high pressure to overcome the pressure of the pumped water. Unfortunately, however, this makes calibration of the injection system difficult as any change in the back pressure of the system affects the output of the injection pump. Low pressure injection injects chemical before the sprayer""s main pump where the pressure remains virtually atmospheric. This allows accurate calibration of the amount of chemical mixed with the water but is slower acting than the high pressure injection since the chemical is injected a significant distance from the spray nozzle.
An object of the present invention is to provide an arrangement which maintains the advantages of low pressure injection of the chemical whilst overcoming or alleviating the disadvantages of the known systems.
According to the invention there is provided spray apparatus of the kind in which chemical to be sprayed is injected into spray liquid before the mixture of liquid and chemical is sprayed e.g. for agricultural use, comprising a closed loop circulating system having a pump with an inlet and an outlet, a loop line connecting the pump inlet and outlet, a spray nozzle connected to the loop line downstream of the pump via a spray line, a spray liquid inlet connected to the loop line upstream of the pump and a chemical injection system connected to the loop line upstream of the pump. The spray apparatus may comprise a venturi device having an inlet and an outlet in the loop line, and having a suction or side port, a return line connection to the spray line at a position adjacent to the spray nozzle and connection to the suction port of the venturi device, an agitation line connected between the loop line downstream of the venturi device and the spray line adjacent the spray nozzle and valve means in the spray line directing liquid flow to the spray nozzle to cause reverse flow through the agitation line past the spray nozzle and through the return line. Further the spray apparatus may comprise a venturi bypass in the loop and bypass valve means in the bypass to control flow through the bypass and thus to control operation of the venturi device.
A container for spray liquid may be connected to the spray liquid inlet.
The spray apparatus may comprise a container for clean washing liquid, and means for connecting the clean washing liquid container to the agitation line to allow washing liquid to be drawn into the agitation line, spray line and the loop line. The spray apparatus may comprise a container for receiving washings, means connecting the washings container to the loop line and washings valve means controlling the connecting means. The clean washing liquid container is preferably the spray liquid container.
From another aspect the invention is agricultural spray means comprising spray apparatus as described above.